In many networks, more often serial interfaces are used instead of parallel interfaces. The reasons for this are the reduction in costs for the layout and connection technology, for example the number of pins, simplification of the system design and scalability of the bandwidth of transmission data by parallel use of a plurality of serial interfaces.
This trend is becoming apparent particularly in the field of consumer electronics with a large number of serial interface standards. Those standards are used mostly for communication with peripheral devices, for example hard drives or displays. Apart from the small number of pins, however, those interfaces make use of complex protocols, which require high expenditure in terms of implementation. For data transmission between logic components (ICs), for example on the mainboard of a PC or within a handheld device, present-day interfaces bundle a plurality of serial data streams, for example PCI-Express or Quickpath, and thereby enable the system designer to scale the bandwidth.
In the automotive engineering sector, serial interfaces (SPI, serial peripheral interfaces) are used for data transmission between logic components, which may be in the form of integrated circuits (IC), in control units. That standard describes bidirectional, synchronous and serial data transmission between a component provided as a master and various components provided as slaves. An interface includes in this case at least three lines between the master and a slave, these normally being two data lines and a clock line. In the case of a plurality of slaves, each of those components requires an additional select line from the master. The SPI interface enables a daisy-chain or bus topology to be implemented.
In some cases, the SPI interface is not suitable for the transmission of time-critical actuation signals in order to meet the real-time requirements of present-day safety applications, for example ESP. Frequently, only an exchange of diagnostic and status information takes place with an SPI interface. Time-critical actuation signals are normally transmitted to the actuation components of the actuators and/or from the evaluation circuits of the sensors at great expense using timer units and/or proprietary interfaces.
When used in the form of a bus topology, at higher data rates the SPI interface gives rise to increasingly poorer signal integrities and high interference due to poor EMC characteristics. Furthermore, only the send signal is transmitted synchronously with the timing signal, whereas phase-synchronous transmission of the receive signal becomes increasingly more difficult as a result of the internal delay times in the slave at high data rates and may cause errors in the data transmission.
When the SPI interface is used in a daisy-chain topology, that is, a ring topology, very high latency times occur, which is why it is not possible for that form to be used efficiently in automotive control units nowadays.
A method for implementing communication in a ring bus is further known from British patent document GB 2 188 216 A. The communications sent between participants of the ring bus have what are commonly referred to as headers which comprise a plurality of digits indicating the availability of the ring bus. In addition, a shift register is provided whose maximum delay represents a number of bits in the header, a control device being able to manipulate data in the header of a message.
A method for transmitting a token in a communication ring is described in German patent document DE 37 88 604 T2. In that instance, a priority level of that token in a communication ring with a plurality of stations is updated. It is provided that each respective range corresponds to priority levels of packets that need to be transmitted by each respective station, the token of the communication ring being transmitted from a first station of the communication ring as soon as a first station transmits a frame containing a packet that is to be transmitted.
There are known from German patent document DE 198 03 686 A1 a method and an apparatus for communication among, for example, equal-access stations of a ring-shaped, serial fiber-optical bus. In that instance, time-cyclical container telegrams are generated, addressed and provided to the serial bus by the stations.